Smoke rings are circular shapes formed by the movement of smoke in the air. They occur when a puff of smoke is released in a specific way, creating a vortex that maintains its shape as it travels. The ring's structure is a result of the air pressure differences inside and outside the ring, allowing it to float and expand as it moves. These rings can be created using various sources of smoke, such as from a cigarette, cigar, or smoke machine. The size and longevity of a smoke ring depend on factors like the amount of smoke, the force of the puff, and environmental conditions like wind.